Solids feeding device



Aug- 23, 1955 N. E. sYLvANDER ETAL 2,716,042

SOLIDS FEEDING DEVICE INVENTOR Nels E. @yh/ander ND 5am 24A/'ones ATTORN EY Aug. 23, 1955 N. E. sYLvANDx-:R ETAL 2,715,042

soLIns FEEDING DEVICE Filed Aug. 18, 1951 2 sheets-sheet 2 INVENTOR Nels i". yA/ander 24A/.1J

Sam gms TTORNEY United States Patent 0 SQLIDS FEEDlNtG DEVICE Nels E. Syivander, Bridgeviiie, and Sam A. Jones, Pittsburgh, Pa., assignors to Pittsburgh Consolidation Coal Company, ittsburgh, Pa., a corporation of Pennsylvania Application August 1S, 1951, Seria No. 242,542

6 Ciaints. (Ci. 392-4@ The present invention relates to an apparatus for feeding particulate solids and more particularly to an apparatus for feeding particulate solids at a constant rate.

Frequently it is desirable or necessary to feed materials at a constant rate. With gases or liquids, constant rate feeding presents few problems. However, when it is attempted to feed divided solid materials at a constant rate, measurement and control dimculties present serious obstacles, which are magniied when in addition, it is desired to feed the divided solids suspended uniformly in a stream of gases.

The primary object of the present invention is to provide an apparatus for feeding particulate solids, and especially finely divided solids, at a constant rate.

Another object of this invention is to provide an apparatus for injecting particulate solids into a stream of gases which serves to transport the solids at a constant rate.

According to our invention, a bed of particulate solids which are to be transported under non-gravity or elevated pressure conditions at a constant rate, is contained in an upright cylindrical vessel which is substantially airtight. The solids on the top of the bed are continuously swept by means of a rotating scraper into the open top of a vertically disposed discharge tube which is caused to descend at a predetermined constant arte. The rotating scraper is in constant engagement with the top layer of the solids bed so that the bed level descends at the said predetermined constant rate.

Carrier gases are introduced into the vessel at a point above the bed level and leave the vessel through the open top of the discharge tube, entraining therein the discharge solids to produce a homogeneous suspension which is delivered through the discharge tube.

While the present invention is particularly adapted to deliver small constant rate quantities of finely divided solids, the apparatus can be employed for feeding large particulate solids at constant rates which are limited only by the size of the apparatus.

For a better understanding of our invention, its operation, other objects and advantages, reference should be had to the following detailed description and to the drawings in which:

Figure l is an end view in elevation and partly in section, of an apparatus embodying our invention;

Figure ll is an enlarged view of a portion of the apparatus shown in Figure I;

Figures Ill, lV, and V are enlarged views of modifications of the paddle arm assembly shown in Figure I;

Figure Vl is an enlarged plan View of that portion of the apparatus which is shown in Figure il.

Referring to Figure l, an airtight cylindrical vessel 10 is mounted in an elevated, upright, vertical position. An opening 12 which can be sealed with a plug 14 is provided in the cylinder shell for introducing a fresh charge of particulate solids into the cylinder. Solids are introduced into vessel 10 to establish therein a bed of solids 16. An elongated cylindrical tube 18, located so that its longitudinal axis substantially coincides with the longitudinal ice axis of the vessel 1Q, is fitted into the vessel 1i) through a stung box 2i).

The discharge tube 18 terminates at its upper end in a lip bearing 44 (see Figure ll). Sleeve member 22 fits slidably around the outside of the discharge tube 18 and rests upon a bearing 46 which is aiiixed to the outer wall of the discharge tube 18. Thus it is seen that the sleeve member 22 is free to rotate about the discharge tube 18 but is prevented from longitudinal motion with respect to the tube by the bearings 44 and 46. A frame work structure 24 encircles the open upper end of the discharge tube 18. A cap member 26, of disc-like configuration is supported in a substantially horizontal plane above the open end of the discharge tube by means of framework structure 24. One or more openings 32 in the framework structure permit carrier gases and solids to pass into the discharge tube 18. Paddle arms 2S aixed to and supported by the framework structure 24,l have pliable tip members 30 of rubber, leather, cloth or the like, adapted to scrape the inner shell of the vessel 10. The bottom edges of the paddle arms 28 should not extend below the bottom of the discharge openings 32 in the framework structure 24.

The driving mechanism for sleeve member 22 and paddle arms 28 can best be understood by reference to Figures ll and Vi which are enlarged sectional views of the sleeve, framework structure, cap and upper discharge tube assembly. Corresponding numerals are employed to indicate corresponding elements.

The sleeve member 22 and the paddle arms 28`are rotated about the longitudinal axis of vessel 10 by means of a drive shaft 34 which is connected to a motor 36 by means of gears 38 and 4). lf, as shown, the driving mechanisxn is located outside the vessel 10, a stung box 42 i is provided to maintain the vessel 1i) airtight.

As can be seen in Figure 6, an opening 48 of uniform square cross section is provided through the cap member 26. Referring again to Figure l, the drive shaft 34 which extends downwardly almost to the bottom of vessel 10, fits slidably through the opening 48 in the cap member 26 and extends downwardly through the center of the discharge tube 18. Drive shaft 34 has a uniform square cross section except at its upper end where a circular cross section is provided to permit rotation of the drive shaft inV the stufng box 42. The drive shaft 34 is associated with the cap 26 in such a fashion that the rotation of the drive shaft will cause rotation of the integral cap, framework structure, sleeve and paddle arm assembly.

The cross-sectional shape of the driving shaft 34 and of the opening 48 in cap member 26 need not be square, although a square cross section is preferred for ease of fabrication. Any non-circular cross-sectional shape in the drive shaft and the opening 48 will be satisfactory so long as the cap member 26 cannot rotate about the drive shaft 34 when said drive shaft is inserted through the opening 48.

Discharge tube 18 is caused to descend at a constant rate by any conventional mechanism. For example, a worm gear, clutch and clamp assembly as shown in Figure i may be used. A clamp member 50 is secured to the discharge tube 18 and is securely associated by means of a connecting eiement 51 with a clutch member 52. A vertical worm gear 54 is rotated by a constant speed motor S6 associated therewith through a set of gears 58 and 60. The clutch member 52 is adapted to engage the worm gear 54 and travel downwardly along said worm gear at a uniform rate when the worm gear rotates at a constant speed. Vertical support members 62 are provided to avoid stresses in the worm gear 54. The clamp 50 also serves to prevent rotation of the discharge tube 18. Y

Carrier gases for transporting solids enter the vessel 1G.

Vwith the wormrgear 54.

VVclutch assembly shown.'

at a predetermined rate through a conduit 64 and pass downwardly through the openings 32 in the frame Work structure 24 into the discharge tube 18 where they pick up the solids which are to .be transported. The solidsin-gas suspension is transportedfrom the discharge tube 18 through a flexible Vconduit 66 into a stationary conduit or directly to the point Vof use. duit` 66 is connected to the discharge tube 18 by means of coupling member 6,8.V

The operation of the apparatus illustrated in Figure I will V,nowl be described. Y

Particulate solids are introduced into vessel 10 through kopening 12 to establish'a bed of solids 16 within the vessel 1t). The discharge tube 18 is positioned so that V the lower edges of the paddle arms 28 make contact with the upper surface of the solids bed V16; The motorV V36'is started, causing the drive shaft 34 to rotate ata constant speed. The drive shaft in turn causes the cap 26, framework structure 24, sleeve member 22 and the Vpaddle arms V23 tol rotate as a unit about the stationary discharge tube 18.V A thin layer of solids from the upperlayer of the bed 16 is scraped by the paddle arms 28 toward the upper end of the discharge tube 18'.- These Vscraped solids reach the center of the upper layer of the bed'and drop through the openings 32 in the framework structure 24 into the discharge tube 18.

The solids which are'discharged during the start-up period, are collected at the bottom of the discharge tube 18 and can be used as feed material for a subsequent Vfeeding Voperation cycle.

After a short period of paddle arm rotation, -the upper surface of the Vsolids bed corresponds to the configuration tube'i18 at a point near the base of the vessel 10. Clutch i member Y52,V is fastened to clamp member 50 by.means of an appropriate connecting element 51 and is engaged After the appropriate stepr down, gears 58 and'60 have been engaged, constant speed Qmotor 56is started, causing worm gear 54 to rotate at a Vconstant speed. Carrier gases are introduced into vessel 10 at a constant predetermined rate through conduit 64. The rotation of worm gearV 54 causes clutch member 52,"connecting element 51, Vclamp member 50 and discharge tube 18 to descend as a unit ata cons Vstant rate determined by the speed motor 56, the stepdown ratio of the' gearsr58 and 60 and the pitch of theV worm gear 54..'

i v Although the wormgear and clutch assembly are used for thepurposes of illustration and are a preferred em-` Y bodiment, nevertheless any convenientmeansmay be ernployedwhich will serve to lower the discharge tube at agconstant'rate. For-example, aV simple winch and cable assembly might be used inrplace of the Worm gear and As theY discharge` tube 18V descends, sleeve member 22 suspended stream through conduit 66 for transportation.

The solids feeding operation continues until the solids comprising the bed 16 have been exhausted. Thereupon the motors 36 and 56 are turned off, clutch member 52 is disengaged from worm gear 54 and the discharge tube 18 is elevated until the paddle arms 28 are near the top of vessel 10. YA fresh charge of solids is'introduced through opening12'and the feeding cycle is repeated.

if desired, a relay contact 70 may be installed to stop the motor 56 Vwhen the clutch member 52 reaches the bottom of the worm gear 54. The downwardly moving clutch member 52 engages the relay contact 70 causingV the motor 56 to turn oi.

In some installations, it may be desirable to install at the bottom of the discharge tube 18 a single telescoping tube instead of the flexible conduit 66 which may not withstand very high'pressures. In fact, where the apparatus is used for feeding lsolids under extremely Velevated pressures, it may be necessary to resort toY a telescoping delivery conduit.

By providing two feeding units in parallel, continuous constant rate solids feeding can be effected through cyclic Y operation in which oneunit is feeding While the other unit is being charged and prepared for the succeeding feeding cycle. Y

The paddle arms employed in the apparatus of this invention can be modified in various formswithout departing Vfrom the spirit of ourV invention. For. example,

t as shown in Figures I and HI, two flat wing-like paddle arms extending oppositely in the same plane may be employed. The lower edges of the paddle arms may be horizontal. Preferably, however, the lower edges of the paddle armsV should be set at Yan angle 0 which can be about 30 but preferably is slightly less than 30;

A modified form of paddle is illustrated in Figure IV. This paddle 72 is constructed of a flat, narrow strip; of sheet metal shaped in the form of a hyperbolic spiral. As shown, the paddle is rotated so that solids are scraped and moved positively toward the center of the containing vessel. With this form of paddle, solids tend to roll in advanceof the paddlearm and collect in the area nearV the top of the discharge tube 18; When high feed rates are employed, solids will collect in such quantities that they` ow over the top of the paddle. This diiculty can be Vcircumvented byY designing the lower edge of the paddleparm 72 so that.V in rotating it generates a cone whose base angle is ape proximately the angle of repose of the solids comprising the bed.

Figure V is a perspectiveiviewof another modified paddle arm structure in which thin, narrow strips of sheet metal formthe paddle arms` 76. A pliable tip member 78 is aiiixed at the end of each arm. Each individual paddle arm radiates upwardly from a framework element 8i). In additionV each paddle arm presentsV a and its integralframework structure 24, capV element A Y 26 andpaddle arms 28 descend at the same rate, and

the rotating'paddle arms continuously scrape a'uniform layery of solidsl from the upper surface of the bed 16.y

Vfactory results.V WeV have found, however, that for a given solid material, slightly higher rates of rotation are concave surface tothe solids bed as the arms rotate.

,The lower edges of each paddle arm generate upon rotation a substantially conical surface whose base angle is slightly less than the repose'angle of the solids.v VThe pliable tip members 78 lcontinuously scrape the inner wall of the containing vessel. lf desired, supporting krods`VV v may bel affixed between the individual arms at points near*V ,Y

the tips of the arms to strengthen the paddle structure.

For additional support, acollar (not shown) with a square cross section opening adapted to engage the paddle` arm drive shaft may be disposed directly above the cap 26 and held in position by aV spider web frame of rods. Y To insure constant rate feeding with our new apparatus,

' one important limitation should beobserved, namely, that no pressure surges be permitted to develop within the cylindrical vessel containing the feed solids. So long as the pressure within the cylindrical vessel is constant, solids will be delivered at a constant rate. ,However, should the pressure decrease suddenly, the vapors in the interstices of the solids bed tend to expand and disperse the particles. In turn, the surface of the bed rises and a sudden surge of solids oods the discharge tube. If the pressure within the vessel is permitted to remain at the decreased value, the solids tend to resume their previous bulk density and the feed rate will resume its predetermined constant rate.

Conversely, when the pressure within the vessel increases suddenly, the solids bed is compacted somewhat and the solids feed rate is reduced until the altered conditions are equalized. Thus, it should be appreciated that the apparatus of this invention cannot tolerate sporadic liuctuations of pressure in the feed solids vessel. The adverse effects of this sensitivity to pressure surges can be minimized by obvious expedients, such as, for example, the installation of back pressure control valves in the solids delivery conduit.

By appropriate designing, the apparatus of the present invention can be adapted to supply solid particles at a constant rate in any desired quantities. The rate of solids delivery, with a feed vessel of given diameter can be accurately controlled by simply controlling the rate at which the discharge tube is caused to descend. For example, with the worm gear and clutch assembly which is the preferred driving mechanism for lowering the discharge tube, the solids feed rate is directly proportional to the rate at which the worm gear rotates. This rotation can be controlled step-wise by providing a series of interchangeable step-down gears; further intermediate control can be achieved by providing a regulatable constant speed driving motor.

With a feeding vessel of given diameter, the rate of paddle arm rotation should be increased slightly as the desired rate of feed is increased so that the paddle arms continuously scrape only a thin layer of solids from the upper surface of the solids bed.

To illustrate further the apparatus of this invention, a specific installation will be described for feeding pulverized coal of -14 Tyler mesh particle size. A l2- inch inner diameter cylindrical vessel was employed as the feed containing Vessel. The discharge tube was a 1/2-inch nominal diameter stainless steel tube. The drive shaft for the paddle arm and sleeve assembly was a AG- inch square rod. Homogeneous solids-in-gas suspensions were obtained at gauge pressures up to about 2O pounds per square inch. The rate of solids withdrawal was uniform in the range from 0.3 lb./hr. to 58 lbs/hr. Carrier gases were introduced at a rate suiiicient to produce a solids-in-gas suspension with a density of 3 lbs./cu ft. or less.

When feeding particulate solids by means of an apparatus according to our invention, it is seen that uniform rates are easily attainable; uneven slugs of solids which would cause high instantaneous feed rates are eliminated. Moreover, the feed solids are not fluidized, but are instead maintained in a xed bed; thus there are no overhead losses of feed solids by elutriation. Our new apparatus can be designed for vacuum or high pressure solids feeding in addition to feeding at normal atmospheric pressures. The feed solids, furthermore, need not be dry in order that a homogeneous suspended solids stream be obtained. Continuous, uniform solids feeding can be eected by installing two or more feeding units in parallel.

According to the provisions of the patent statutes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims,

d the invention may be practised otherwise than as specifically illustrated and described.

We claim:

l. An apparatus for feeding particulate solid material at a constant rate comprising an upright cylindrical vessel adapted to coniine a bed of particulate solids, an elongated gravity feed discharge tube substantially centrally positioned within said vessel and extending vertically through a substantially airtight seal in the bottom wall of said vessel, a supporting structure rotatable about the upper terminus of said discharge tube and incapable of longitudinal motion with respect to said discharge tube, said supporting structure having lateral openings therein to permit the iiow of solids therethrough into open top of said discharge tube, at least one paddle arm afxed to and supported by said rotatable supporting structure, said paddle arm being positioned with respect to the open top of said discharge tube to cause, upon rotation of said supporting structure, a movement of from the surface of said solids bed into the open top of said discharge tube, iirst mechanical driving means for rotating said rotatable supporting structure and second mechanical driving means independent of said first mechanical driving means for causing said discharge tube and said supporting structure to descend at a constant rate.

2. An apparatus for feeding particulate solid material at a constant rate comprising an upright substantially airtight cylindrical vessel having a top wall and a bottom wall and being adapted to confine a bed of particulate solids, an elongated gravity feed discharge tube substantia ly centrally positioned within said vessel and extending vertically through a substantially airtight seal in the bottom wall ot' said vessel, a rotatable sleeve member adapted to rotate about the upper terminus of said discharge tubeV and incapable of longitudinal motion with respect to said discharge tube, a framework structure atiixed to and supported by said sleeve member and extending upwardly above the upper'terminus of said discharge tube, a cap member immovably aiiixed to said framework structure, at least one paddle arm immovably afiixed to said framework structure and extending radially to contact with the inner wall of said vessel, said paddle arm being positioned with respect to the open top of said discharge tub: to cause, upon rotation of said framework structure, a movement of solids from the surface of said solids bed into said open top of said discharge tube, means for rotating said sleeve, framework structure, cap and paddle arm as a unit about the longitudinal axis of said vessel, mechanical driving means for causing said discharge tube to descend at a constant rate, and means for introducing carrier gases into said vessel.

3. The apparatus ot' claim 2 in which the lower edge of each paddle arm generates upon rotation a geometric cone whose base angle is in the range from 0 to an angle equal to the angle of repose of the solid material comprising the bed of solids in said vessel.

4. An apparatus for feeding particulate solid material at a constant rate comprising an upright substantially airtight cylindrical vessel having a top wall and a bottom wall and being adapted to confine a bed of particulate solids, elongated gravity feed discharge tube substantially centrally vertically positioned within said vessel and extending upwardly through a substantially airtight seal in the center of the bottom wall of said vessel, a rotatable sleeve member adapted to rotate about the upper terminus of said discharge tube and incapable of longitudinal motion with respect to said discharge tube, a frameworl/` structure aixed to and supported by said sleeve member and extending upwardly above the open upper terminus of said discharge tube, a cap member immovably atxed to said framework structure, at least one paddle arm immovably aixed to said framework structure and extending radially outwardly, a pliable tip at the radial extremity of said paddle arm adapted to Y make continuous contact with the inner side Wall of Y said vessel, said paddle arm being positioned with respect 'to the open top of said discharge tube to cause, upon rotation of Vsaid framework structure, a movementl of solids from the surface of said solids bed into said open top ofsaid solids dischargetube, a drive shaft of noncircular cross section substantially centrally positioned withinV said vessel and extending vertically downwardly into said discharge tube through a channel extending vertically throughlthe top wall rof said cap member, the cross section` of said channel being similar tothat of said drive shaft so that said cap member is free'to slide longitudinally along said drive shaft but cannotrrotate about said drive shaft, means for rotating said drive shaft, mechanical driving `means nfor causing said discharge tube to descend ata constant rate, and means for introducing Y carrier gases into said vessel.

Y5.y An apparatus for feeding particulate solid material at a constant rate comprising an upright substantially airtight cylindricalvvessel having a top wall and a bottom wall, adapted to confine a bed of particulate solids, angelongated discharge tube substantially centrally ver- Y ticallyfpositioned within said vessel and'extending npwardly through a substantially airtight seal in the center of the bottom wall of said vessel, a rotatable sleeve member adapted to rotate about the upper terminus of said discharge tube and incapable of longitudinal motion with Vrespect to said discharge'tube, a framework structure aixed to and supported by said sleeve member and exa tending upwardly above the upper terminus of said discharge tube, a cap member immovably ai'lixed to said framework structure, at least one paddle arm immovably aiiixed to said framework structure and extending radially outwardly,l a pliable tip at theV radial extremity of said paddle arm adapted to make continuous contact with the `inner side wall of said vessel, means for Vrotating said sleeve, framework structure, cap and paddle armas a unit about the longitudinal axisY of said vessel, a clamp adapted to be axed to said discharge tube at a point external toV said vessel, a vertically disposed worm gear, means for causing said worm gear to rotate at a constant speed, a

clutch member adapted to engage said wormrgear and to-move longitudinally downward along said Worm gear vwhen said worm lgear is rotated, means for securing said clutch member to said clamp, and means for introducing carrier gases into said vessel.

6. In an apparatus for feeding particulate solids aty constant rates, the combination comprising a vertically disposed solids discharge tube open at both ends, adapted for vertically longitudinal motion only, a rotatable sleeve'. member adapted to encircle said discharge tube at its upper terminus, adapted to rotate about saidV discharge'V tube and secured to prevent longitudinal motion with respect to said tube, a framework structure having lateral openings therein to permit the passage of particulate solids therethrough, said structure affixed to and supported by Y said sleeve and extending longitudinally above the upper terminus of said discharge tube, a cap member of disc- Y like configuration havingV a` non-circular vertical opening therethrough, said cap member disposed perpendicularly to the longitudinal axis of said discharge tube and aixed to and supported by said framework struct-ure, at least onetpaddle arm aiiixed to and supported by said framework structure and extending radially outwardly therefrom, a vertically disposed drive shaft of non-circular cross section, slidably engageable with the opening in said cap member and depending into said discharge tube, said drive shaft incapable of rotationwith respect to said cap member, and meansrfor rotating said drive shaft.

References Cited in the file of this patent Y Great Britain Sept. 2l, 1942 

